(1)Field of the Invention
The present invention relates to wireless communications systems, and more particularly to data and voice communications systems utilizing an advance mobile phone system (AMPS) cellular network.
(2) Description of the Related Art
Referring to FIG. 1, to provide communications over a telephone network, a data communication network system includes a computer host 12 and a modem 14 that is connected to a wall socket of a phone line so that data from modem 14 can be transmitted to a telephone network 16. A second modem 18 is provided to receive the data from modem 14. Modem 18 receives the data from telephone network 16 and sends it to a computer host 20. The system shown in FIG. 1 is a typical data communication network system for a wired telephone network.
A conventional wireless communication network system is shown in FIG. 2. The wireless network system includes a computer host 22, a modem 24, a modem interface 26, a cellular phone 28, and a base station 30. The wireless system is typically coupled to telephone network 16, modem 18 and computer host 20. In this instance, modem 18 is a landline modem. In another instance, telephone network 16 may be replaced by a cellular phone and a modem interface in which modem 18 is a mobile modem. To transmit data from computer host 22 to computer host 20, the data in computer host 22 is sent to cellular phone 28 through modem 24 and modem interface 26. Cellular phone 28, in turn, transmits the data to base station 30. Base station 30 then transmits the data to telephone network 16 which sends the data to computer host 20 through modem 18. Because modem 24 of FIG. 2 is the same as modem 14 of FIG. 1, modem interface 26 is required in the network system shown in FIG. 2. Because of modem interface 26, node 25 has the same characteristics as node 15 of FIG. 1. Modem interface 26 provides an analog path with appropriate protocols to make cellular phone 28 and base station 30 appear as a landline telephone network. Modem interface 26 is used to convert the signal at node 25 which is outputted by modem 24 into a signal that is compatible with cellular phone 28. Also, modem interface 26 converts the signal outputted by cellular phone 28 at node 27 into a signal that is compatible with modem 24. For instance, when computer host 22 tries to dial a number, modem 24 produces a tone dialing signal at node 25. However, cellular phone 28 cannot accept the tone dialing signal as an input. Thus, modem interface 26 converts the tone dialing signal into another form that can be received by cellular phone 28.
In FIG. 2, modem 24 can be made internal or external to computer host 22. Modem interface 26 can be an external device or an internal device built into modem 24 or cellular phone 28.
FIG. 3a is a detailed block diagram of modem 24, modem interface 26 and cellular phone 28 of FIG. 2. Modem 24 includes a system control A 43, a host interface 42, a data pump 44, a digital-to-analog (D/A) and analog-to-digital (A/D) converter 45, and a data access arrangement (DAA) 46. System control A 43 controls and operates host interface 42, data pump 44, D/A & A/D converter 45 and DAA 46. Data pump 44 modulates data coming from computer host 22 of FIG. 2 and demodulates signals coming from cellular phone 28. The D/A is used to convert digital signals from data pump 44 into analog signals, and the A/D is used to convert analog signals coming from cellular phone 28 into digital signals for data pump 44. DAA 46 is used as a protective connecting device that serves as an interface between D/A & A/D converter 45 and modem interface 26.
Cellular phone 28 in FIG. 3a includes a system control B 53 for controlling and operating the components in cellular phone 28--an analog cellular transceiver 50 and a radio transceiver 52. To send data, analog cellular transceiver 50 receives analog signals from modem interface 26, processes the signals in an analog domain and generates signals that can be converted into radio waves. To receive data, radio transceiver 52 receives radio waves, converts the radio waves into analog signals so that analog cellular transceiver 50 can process them in the analog domain.
The wireless communication system shown in FIG. 3a has several disadvantages. First, because the wireless communication system uses an analog cellular transceiver whose characteristics are optimized for voice communication but not for data communication, data communication rate is low. Second, because a signal conversion (i.e., analog-to-digital or digital-to-analog) occurs between two signal processing units (data pump 44 and analog cellular transceiver 50), signals tend to degrade, causing errors. Ideally, all signals should be processed in one domain (e.g., either digital or analog), and be converted into another form either at the beginning or at the end of the signal processing to avoid signal degradation. In the system shown in FIG. 3a, to send data, data pump 44 processes digital signals, D/A & A/D converter 45 converts the digital signals into analog signals, and analog cellular transceiver 50 processes the analog signals that are degraded. When signals are converted from a digital to an analog form (or from an analog to a digital form), the signals become degraded because the conversion process loses some information in the signals, and noise is injected into the signals. When the degraded signals are processed further, they may further reduce performance. Third, because modem 24 and cellular phone 28 operate under two separate system controls, modem 24 cannot adapt to dynamic changes that occur in cellular phone 28, and cellular phone 28 cannot adapt itself to the changes that occur in modem 24. A wireless communication system shown in FIG. 3a which is connected to an AMPS cellular network allows only the modem analog data and the emulated PSTN type information (ringing, busy, etc.) to be transferred between modem 24 and cellular phone 28. In effect, modem 24 sees the cellular telephone channel as a landline telephone channel. In addition, currently existing cellular protocols such as NMP10 and ETC are blind to the dynamic characteristics of the cellular telephone channel.
A prior art wireless communications system shown in FIG. 3b is similar to the one shown in FIG. 3a except that it uses a digitally implemented cellular transceiver 72 instead of an analog cellular transceiver. Because cellular transceiver 72 is digital, it may process signals more accurately than analog cellular transceiver 50. However, because the wireless communication system uses digital implementation, the system requires two extra A/D & D/A converters. Thus, the system in FIG. 3b may require more hardware than the system shown in FIG. 3a. The system in FIG. 3b has similar disadvantages as the one shown in FIG. 3a. Because of D/A & A/D converters 65 and 70, digitally implemented cellular transceiver 72 receives and processes degraded signals. Data degradation may be greater in this instance because the system requires two conversions to send signals from data pump 64 to digitally implemented cellular transceiver 72. In addition, like the system in FIG. 3a, the system in FIG. 3b includes two system control units: system control A 63 for modem 24 and system control B 73 for cellular phone 28. Because modem 24 and cellular phone 28 are controlled by two separate system controls, as described before, modem 24 cannot adapt to the dynamic changes that occur in cellular phone 28, and cellular phone 28 cannot adapt to the changes that occur in modem 24.
It will be advantageous, therefore, to provide a wireless communication system (a) having one system control unit for all the components of the system so that the various components of the system can be adapted and adjusted as the parameters of the other components or the dynamic characteristics of the cellular channel vary and (b) performing all of the signal processing in one domain to reduce signal degradation. In the present invention, a wireless communication system operating under one system control unit provides a way to implement advanced protocols that take advantage of control channel information and messages that are passed between a base station and a cellular transceiver.